This invention generally relates to the field of paper making, and more specifically, to paper machine substrates.
Different types of pulp feedstocks may be used for making paper. Some feedstocks, such as recycled paper, often have contaminants. These contaminants include dirt and stickies. Stickies consist primarily of organic adhesives used in the paper converting industry, such as hot melts, pressure-sensitive adhesives, expanded polystyrene, and lattices. Generally, stickies include polyvinyl acetate polymers and copolymers, ethylene vinyl acetate polymers and copolymers, polystyrene, styrene-butadiene, polypropylene, polyethylene, polyamide, latex, other rubber compounds, and wax. A common source of stickies is the tackifiers added to paper products to improve adhesion properties.
Unfortunately, these stickies often adhere to the paper machine substrates, such as press felts, fabric sheets, and forming wires, that transport the pulp fibers during the paper making process. Once adhered to the paper machine substrate, the stickies may create holes in the substrate, and thus, may affect the quality of the produced paper. Furthermore, continued stickies deposition may require the replacement of the substrate, and thereby, increase production costs.
Accordingly, a paper machine substrate that resists stickies adhesion will improve over conventional paper machine substrates.
As used herein, the term xe2x80x9ccomprisesxe2x80x9d refers to a part or parts of a whole, but does not exclude other parts. That is, the term xe2x80x9ccomprisesxe2x80x9d is open language that requires the presence of the recited element or structure or its equivalent, but does not exclude the presence of other elements or structures. The term xe2x80x9ccomprisesxe2x80x9d has the same meaning and is interchangeable with the terms xe2x80x9cincludesxe2x80x9d and xe2x80x9chasxe2x80x9d.
As used herein, the term xe2x80x9cpaper machine substratexe2x80x9d refers to a surface for transferring a layer of a different material, such as a fiber slurry or web. Examples of paper machine substrates include forming wires and press felts. Other examples of paper machine substrates include through-dryer, forming, and transfer belts as disclosed in U.S. Pat. No. 5,048,589, which is hereby incorporated by reference. Materials used to manufacture paper machine substrates include metals, such as steel or iron; mineral fibers, such as extruded glass or ceramics; natural fibers, such as wool; polymers; or mixtures thereof. Polymers used to manufacture substrates include polyolefins, such as polyethylene or polypropylene; polyamide polymers, such as nylon; and polyesters, such as polyethylene terephthalate; or mixtures thereof. Desired substrates can be made from woven polyethylene terephthalate or nylon, or alternatively, may be made from stapled substrates, such as woven polyethylene terephthalate sewn with nylon.
As used herein, the term xe2x80x9cforming wirexe2x80x9d refers to a screen belt or fabric on any wet-type paper machine. Liquid is drained from the pulp slurry deposited on the belt as the paper sheet is formed. Forming wires may be made of materials including metals, mineral fibers, natural fibers, polymer fibers, or mixtures thereof.
As used herein, the term xe2x80x9cpress feltxe2x80x9d refers to a continuous belt that performs as a conveyor or transmission belt of a pulp sheet, provides a cushion between press rolls, and serves as a medium for removal of liquid from the pulp sheet.
As used herein, the term xe2x80x9cgraftedxe2x80x9d refers to the bonding, such as covalent bonding, of one material to another. An exemplary grafting technique chemically bonds organic polymers to a wide variety of other materials, both organic and inorganic, in the form of fibers, films, chips, particles, or other shapes.
As used herein, the term xe2x80x9cactive agentxe2x80x9d refers to a substance that grafts or bonds to a paper machine substrate. Exemplary active agents include fluorinated monomers, fluorinated polymers, perfluorinated polymers, and polyalkyl siloxanes.
The term xe2x80x9cmachine directionxe2x80x9d as used herein refers to the direction of travel of the forming surface onto which fibers are deposited during formation of a material.
The term xe2x80x9ccross-machine directionxe2x80x9d as used herein refers to the direction that is perpendicular and in the same plane as the machine direction.
As used herein, the term xe2x80x9cwovenxe2x80x9d refers a network of crossed and interlaced material.
As used herein, the term xe2x80x9cnonwoven webxe2x80x9d refers to a web that has a structure of individual fibers which are interlaid forming a matrix, but not in an identifiable repeating manner. Nonwoven webs have been, in the past, formed by a variety of processes known to those skilled in the art such as, for example, meltblowing, spunbonding, wet-forming and various bonded carded web processes.
As used herein, the term xe2x80x9cspunbond webxe2x80x9d refers to a web formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries with the diameter of the extruded filaments then being rapidly reduced, for example, by fluid-drawing or other well known spunbonding mechanisms. The production of spunbond nonwoven webs is illustrated in patents such as Appel, et al., U.S. Pat. No. 4,340,563.
As used herein, the term xe2x80x9cmeltblown webxe2x80x9d means a web having fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten fibers into a high-velocity gas (e.g. air) stream which attenuates the fibers of molten thermoplastic material to reduce their diameters. Thereafter, the meltblown fibers are carried by the high-velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed fibers. The meltblown process is well-known and is described in various patents and publications, including NRL Report 4364, xe2x80x9cManufacture of Super-Fine Organic Fibersxe2x80x9d by V. A. Wendt, E. L. Boone, and C. D. Fluharty; NRL Report 5265, xe2x80x9cAn Improved Device for the Formation of Super-Fine Thermoplastic Fibersxe2x80x9d by K. D. Lawrence, R. T. Lukas, and J. A. Young; and U.S. Pat. No. 3,849,241, issued Nov. 19, 1974, to Buntin, et al., which are hereby incorporated by reference.
As used herein, the term xe2x80x9ccellulosexe2x80x9d refers to a natural carbohydrate high polymer (polysaccharide) having the chemical formula (C5H10O5)n and consisting of anhydroglucose units joined by an oxygen linkage to form long molecular chains that are essentially linear. Natural sources of cellulose include deciduous and coniferous trees, cotton, flax, esparto grass, milkweed, straw, jute, hemp, and bagasse.
As used herein, the term xe2x80x9cpulpxe2x80x9d refers to cellulose processed by such treatments as, for example, thermal, chemical and/or mechanical treatments.
As used herein, the term xe2x80x9cslurryxe2x80x9d refers to a liquidity, such as watery, mixture or suspension of insoluble matter, such as pulp.
As used herein, the term xe2x80x9cfiberxe2x80x9d refers to a fundamental solid form, usually crystalline, characterized by relatively high tenacity and an extremely high ratio of length to diameter, such as several hundred to one. Exemplary natural fibers are wool, silk, cotton, and asbestos. Exemplary semisynthetic fibers include rayon. Exemplary synthetic fibers include spinneret extruded polyamides, polyesters, acrylics, and polyolefins.
As used herein, the term xe2x80x9cweight percentxe2x80x9d refers to a percentage calculated by dividing the weight of a material of a mixture by the total weight of the mixture and multiplying this quotient by 100.
As used herein, the term xe2x80x9cpercent add-onxe2x80x9d refers to the percent of material added to a substrate after undergoing a treatment. The percent add-on is calculated by subtracting the pre-treatment weight (Wo) from the dried post-treatment weight (Wt) and dividing this difference by the pre-treatment weight (Wo). This quotient is than multiplied by 100 to obtain the percent add-on. A formula for calculating the percent add-on is depicted below:       Percent    ⁢          xe2x80x83        ⁢    Add    ⁢          -        ⁢    on    =                              (                      W            t                    )                -                  (                      W            o                    )                            (                  W          o                )              *    100  
As used herein, the term xe2x80x9cpercent reduction in bond strengthxe2x80x9d refers to the percent reduction in maximum peel load by calculating the maximum peel load difference between a treated and an untreated substrate, dividing this difference by the maximum peel load of the untreated substrate, and multiplying this quotient by 100.
As used herein, the term xe2x80x9cpeel strengthxe2x80x9d refers to the maximum peel load, expressed in grams, required to separate tape from a paper machine substrate at about 180 degree angle over a distance of 2 inches (5.08 centimeters).
The problems and needs described above are addressed by the present invention, which provides a paper machine substrate. The paper machine substrate may include a grafted active agent that lowers the surface energy of the paper machine substrate for resisting the adhesion of stickies. Furthermore, the paper machine substrate may have a permeability sufficient to permit the passage of water therethrough. Moreover, the paper machine substrate may further include a polymer, such as polyethylene terephthalate or nylon. Also, the paper machine substrate may further include a metal. What is more, the substrate may have a surface energy sufficiently low to exhibit repellency to isopropyl alcohol.
In addition, the grafted active agent may be a fluorinated monomer. Some fluorinated monomers may have the chemical formula:
CH2xe2x95x90CROCO(CH2)x(CnF2n+1) 
wherein n is an integer ranging from 1 to 8, x is an integer ranging from 1 to 8, and R is H or CH3. What is more, the fluorinated monomer may be selected from the group including 2-Propenoic acid, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl ester; 2-Propenoic acid, 2-methyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl ester; 2-Propenoic acid, pentafluoroethyl ester; 2-Propenoic acid, 2-methyl-, pentafluorophenyl ester; Benzene, ethenylpentafluoro-; 2-Propenoic acid, 2,2,2-trifluoroethyl ester; and 2-Propenoic acid, 2-methyl-, 2,2,2-trifluoroethyl ester.
Alternatively, the grafted active agent is selected from the group comprising fluorinated polymers, perfluorinated polymers, and polyalkyl siloxanes.
Another embodiment of the present invention is a process of making a treated paper machine substrate. The process may include the steps of providing a paper machine substrate, applying an active agent to the paper machine substrate, and exposing the paper machine substrate to greater than about 2 million rads (Mrad) of radiation.
Furthermore, the paper machine substrate may have a permeability sufficient to permit the passage of water therethrough. In addition, the paper machine substrate may further include a polymer, such as polyethylene terephthalate or nylon. What is more, the paper machine substrate may further include a metal.
In addition, the active agent may be a fluorinated monomer. Some such fluorinated monomers may have the chemical formula:
CH2xe2x95x90CROCO(CH2)x(CnF2n+1) 
wherein n is an integer ranging from 1 to 8, x is an integer ranging from 1 to 8, and R is H or CH3. The fluorinated monomers may be selected from the group including 2-Propenoic acid, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl ester; 2-Propenoic acid, 2-methyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl ester; 2-Propenoic acid, pentafluoroethyl ester; 2-Propenoic acid, 2-methyl-, pentafluorophenyl ester; Benzene, ethenylpentafluoro-; 2-Propenoic acid, 2,2,2-trifluoroethyl ester; and 2-Propenoic acid, 2-methyl-, 2,2,2-trifluoroethyl ester.
Alternatively, the active agent is selected from the group comprising fluorinated polymers, perfluorinated polymers, and polyalkyl siloxanes.
Another embodiment of the present invention is a treated paper machine substrate. The treated paper machine substrate may be made by the steps including providing a paper machine substrate and grafting an active agent to the substrate that lowers the surface energy of the paper machine substrate for resisting the adhesion of stickies.
The present invention may be used to modify paper machine substrates, such as forming wires, press felts, and through-dryer belts. These substrates may be manufactured from metals, such as steel or iron, natural fibers, such as wool, polymers, or mixtures thereof. Polymers used to manufacture substrates may include polyolefins, such as polyethylene or polypropylene, polyamide polymers, such as nylon, and polyesters, such as polyethylene terephthalate, or mixtures thereof. Generally, the paper machine substrates are woven materials permitting the passage of water therethrough.
In one desired embodiment, the paper machine substrates are modified by applying a solution and exposing the treated substrate to gamma rays, or desirably, electron beam induced grafting. The solution may include an active agent and solvent. Active agents may include fluorinated monomers, fluorinated polymers, perfluorinated polymers, and polyalkyl siloxanes.
Exemplary fluorinated monomers include 2-Propenoic acid, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl ester; 2-Propenoic acid, 2-methyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8, 8-pentadecafluorooctyl ester; 2-Propenoic acid, pentafluoroethyl ester; 2-Propenoic acid, 2-methyl-, pentafluorophenyl ester; Benzene, ethenylpentafluoro-; 2-Propenoic acid, 2,2,2-trifluoroethyl ester; and 2-Propenoic acid, 2-methyl-, 2,2,2-trifluoroethyl ester.
Other fluorinated monomers that may be used in the solution have the general structure of:
CH2xe2x95x90CROCO(CH2)x(CnF2n+1) 
wherein n is an integer ranging from 1 to 8, x is an integer ranging from 1 to 8, and R is H or CH3. In many instances, the fluoroacrylate monomer may be comprised of a mixture of homologues corresponding to different values of n.
Monomers of this type may be readily synthesized by one of skill in the chemical arts by applying well-known techniques. Additionally, many of these materials are commercially available. The DuPont Corporation of Wilmington, Del. sells a group of fluoroacrylate monomers under the trade name ZONYL(copyright). These agents are available with different distributions of homologues. More desirably, ZONYL(copyright) agents sold under the designation xe2x80x9cTA-Nxe2x80x9d and xe2x80x9cTMxe2x80x9d may be used in the practice of the present invention.
Solvents used in the present invention may include halogens, ketones, esters, such as ethyl acetate, and ethers, such as diethyl ether, and water. Halogens may include chloroform, methylene chloride, perchloroethylene, and halogens sold under the trade designation FREON(copyright) by the DuPont Corporation. Ketones may include acetone and methyl ethyl ketone.
The weight percent of active agent in solution may range from about 0.1 percent to about 50 percent. Desirably, the weight percent of active agent in solution may range from 9 about 0.5 percent to about 20 percent. More desirably, the weight percent of active agent in solution may range from about 1 percent to about 10 percent.
After impregnating or saturating the paper machine substrates with the solution, the substrates are exposed to electron beam radiation, which results in the grafting of the active agent to the substrate. One exemplary electron beam apparatus is manufactured under the trade designation CB 150 ELECTROCURTAIN(copyright) by Energy Sciences Inc. of Wilmington, Mass. This equipment is disclosed in U.S. Pat. Nos. 3,702,412; 3,769,600; and 3,780,308; which are hereby incorporated by reference.
Generally, the substrates may be exposed to an electron beam operating at an accelerating voltage from about 80 kilovolts to about 350 kilovolts. Desirably, the accelerating voltage may be from about 80 kilovolts to about 250 kilovolts. More desirably, the accelerating voltage is about 175 kilovolts. The substrate may be irradiated from about 0.1 million rads (Mrad) to about 20 million rads (Mrad). Desirably, the substrates may be irradiated from about 0.5 Mrad to about 10 Mrad. More desirably, the substrates may be irradiated from about 2 Mrad to about 5 Mrad.
Alternatively, the active agent, such as ZONYL(copyright) TA-N agent may be heated to liquid form. This liquid may be applied with or without a solvent, such as acetone, directly to the substrate with vacuum assistance. Once the monomer is applied the substrate, it could be irradiated.
Generally, if the substrate is a polymer, the electron beam radiation causes a reaction between the active agent and substrate. As a result, the active agent may become grafted and/or crosslinked to the substrate.